Method of and means for preventing radiation and extra reradiation in radioreceivers



June 3, 1930. BALLANTlNE I 1,760,871

METHOD OF AND MEANS FOR PREVENTING RADIATION AND EXTRA RERADIATION INRADIORECEIVERS. Y

Filed June 17, 1924 2 Sheets-Sheet 1 Ll FF/(L571.

1 z I a ya June 3,- 1930. -s. BALLANTINE 1,760,871

METHOD OF AND MEANS FOR PREVENTING RADIATION v AND EXTRA RERADI'ATION INRADIOREGEIVERS Filed June .17, 1924 2 Sheets-Sheet 2 a {|I|||||||| *t J-L5. A 4 7-63 3 ml "2-- c c017 Aa/am v 7; & Mu'd/rach'om/ a v MnJupmrvdyno mow I i v 1:): Q glwue'ntot; MW I A %A :-8 L L 6,2 al bi new;

the reradiation less perhaps by a ever, by the method of this'invention.

Patented lune 1 930 UN- ITED STATES PATENT OFFICE;

STUART BALLANTINE, OE MOUNTAIN LAKES, JERSEY, ASSIGNOB OF ONE-Em TORADIO FREQUENCY LABORATORIES, INCORPORATED, OF BOONTON, NEW JERSEY,

a conrona'rron or NEW JERSEY METHOD OF AND FORIPBEV'ENTING RADIATION ANDEXTRA BADIOBEQEIVEBS nals. In theforme'r case the regeneration is usedto amplify the signal; in the latter case the regeneration 1s pushed tothe point of oscillation and the signal is rendered audible by theheterodyne beating of the local'and signal oscillations. The latteraction is employed also in the so-called superheterodyne method ofreception in which the signal irequency is lowered previous toamplification. In the present practice the regenerative or oscillatoryelements of the receiver affect-the current in the antenna and causeeither radiation or extra reradiation. Radiation is caused when thelocal-generation of energy is quite independent of the incoming signal.An example of this is a regenerative receiver which is allowed tooscillate. Extra reradiation is due to the regenerative efiect in theantenna,

and is distinguished. from normal rel-adiation. The normal reradiationis the-natural reflection from the antenna system, no regeneration beingpresent. It is equal to the square of the antenna current multiplied byresistance. When regeneration is present the antenna current isincreased or decreasedfirom its normal value and the reradiation ischanged from its normal amount ;-the difierence is calledthe extrajreradiation in this'discussion.

Whileall reradiation aflectsanother neighboring antenna structure andreceiver and may become undesirable, yet the normal reradiation cannotvery well be eliminated unspeciallyfrequency independentregenerativeincrease of antenna resistance or try of the antenna. Both the extrareradiation may be eliminated, how- Such an object is very desirable,since radiation can interfere with the proper reception 0 signals atother nearby stations. With the present-day congestion of radioreceivers, re-

0 radiating receivers are a very general nuiis to provide will beapparent from the by actually a terin'g the geonrethe radiation andaudion repeater element A .Aprlicafionrleaiune 17, 1924.1. 720,708. I

s'ance, especially 'in connection with radio telephone reception. 7

As the regeneration can point of oscillation, both the regenerative andthe oscillatory elements self-oscillation but for convenience ofdescription the simpler expression oscillatory elemen will be used inthefollowing specificat-ion and claims tive as well as true oscillatoryelements such as are purposely employed in heterodyne reception.

-' An object ofthe invention is to provide a radio receiver in whichthe'amplification of be forced' to the- I of receiving sets can bedefined as -elemcntscapable of sustained in reference to regenera-'BEBADIATION. IN

the current or generation of other currents in the antenna or othercollecting device by an oscillatory element is eliminated. object aradio receiver including an oscillatory element, but which will notcause undesirable extra reradiation. A further object of the inventionis to pro 'de a radio receiver in which a substantially perfectly onewayrepeater element is located between the Y current collecting element.More specifically an object of the invention is to provide asubstantially perfectly one-way audion repeater.

These and other objects of the invention following specification whenconsidered in connection with the accompanying drawings, in which Fig. 1is a diagram showing the schematic organization ofth'e invention;

Fig. 2 is acircuit diagram showing an means and an oscillatoryaudionrepeater element with arrangements for-rendering itunidirectional, the effects of capacity coupling being eliminated by acornpensation method;

Fig. 3 is a circuit diagram of a modifica tion of the circuit of Fig. 2y

Fig. 4 is a circuit diagram showing an audion repeater element witharrangements for rendering it unidirectional, a capacity coupl ngbeingFig. 5 is a circuit diagram'showing an with arrangements eliminated byan f alternative compensation method;

ion

capacity coupling being eliminated by a neutralization method;

Fig. 6 is a circuit diagram showing an audion repeater element witharrangements for rendering it unidirectional, the effects of capacitycoupling being eliminated by a modified Hazeltine neutralization method.

Fig. 7 is a circuit diagram showing the re.- lation. of theunidirectional repeater element of the type of Fig. 2 to an antenna andregenerative receiver of conventional type.

Fig. 8 is a circuit diagram showing the uni-' directional repeaterelement of the type of Fig. 2 used with a coil antenna andsuperheterodyne receiver of conventional type.

I shall now proceed to describe my invention with reference to a numberof specific embodiments, giving, for the sake of a clear disclosure,definite constants and relations. I wish it to be distinctly understood,however, that my invention is in no way limited to the specificembodiments hereiii recited or to Cir-- cuit constants or other valueshere given;

The fundamental organization of the in- Theantenha is brought toresonance with the signal tdbe received y means of theantenna tuning aparatus 1. The tuning network is designed to furnish to the inputterminals of the unidirectional repeater 2 a high voltage and smallcurrent. Thisis amplified by the repeater and passed on, throughsuitable coupling impedanccs, to the receiving apparatus 3. The receivercontains oscillatory elements which will in general cause large currentsto flow in the plate circuit of the umdirectional the device beunidirectional. By the term uni-w repeater. For the success of theinvention it is necessary that these currents be prevented fromestablish ng any difference of potential across the input terminals, inother words, that directiona repeater or unidirectional audion stageasherein used, I mean a repeater or andion. stage which while peratingover a predeterm ned frequency range will transmit impressedoscillations in one'direction, but will not to any appreciable e enttransmit oscillations inthe reverse direction. If this repeater is ofthe audion type and properly designed to F it not only attainsthe'ob'ject of the invention butfserves as a stage of amplification aswell I and is of-two-fold utility. The'audion repeater element isrendered perfectly unidiree-j tional by providing isilpecial means -foreliminating the efiect of e current in theplate circuit upon the gridcircuit, to which the antenna is connected. (In this discussion the termantenna is used generically to denote the collecting means, of whateverform.) An

ordinary audion repeater will not do on account of several actions whichwill be explained presently.

these is the capacity the capacit V trodes of coupli engendered bybetween the:gri and plate elece audion, and between the Wires betweenthe coils or current through the The most important of and apparatusconnected to these electrodes. The extra-audion capacity can be largelyeliminated by shielding, as is well known to those skilled in the art;the efiects of the intro- I due to the capacity between grid andplateelectrodesof the audion and their connections;

2. On account of the flow of ions or electrons from the filament to thegrid of the 3; On account of the coupling due to the flow. of the plate(thermionic) current throu h the filament; vention is shownschematically in Fig. 1.' 4. 5

maccount of the charge induced upon the grid charge 5. On account ofcondensers and their connections on either side of the repeater tube.

he, capacity coupling is compensated or neutralized by the generalmethods disclosed in my copending application or by the specific methodsdisclosed in the patent to Rice N 0. 1,334,118, 'or the patents toHazeltine Nos. 1,450,080 and 1,489,228.

The coupling due, to the effect of the varying plate voltage upon anythermionic current that may be. flowing from filament to grid may beeliminated by biasing the grid and otherwise choosing the normalelectrode voltages so that the smallest possible grid curelectrode bythe varying, space any incidental coupling rent flows in the range ofgrid voltage impressed-upon the device. This is sometimes .accomplisedby connecting the grid return to the negative terminal of thefilament; in other cases it may benecessary to insert a csfln y I I Theefiectupon the grid circuit of the plate filament arises from the toresistance of the filament and is of importance only in the case oftubes having high resistance filaments. Examples of this are the audionslmown to the trade as Type [TV-201A, which have filament resistancesbetween terminals of the order of 20 ohms. If

the plate return connects to one filament terminal the alternat' platecurrent flowin through the filament will cause the potential of everyother. part of the filament, with respect to this terminal, to vary,with the result that a varying charge is induced u on the grid. I pro tothis e ect y allowing the b tern I constituent of the plate current toenter t at both terminalsl This may be accom lished by shunting thefilament terminals y a large condenser, the impedance of this condenserto the currents to be amplified being very small compared with theresistance of the filament and of the A batter and its connections 'Acapacity of theord er of one microfarad is indicated at a frequency ofone million cycles (300 meter wave length).

The effect of the varying space charge upon the charge induced upon thegrid electrode resembles that due to the grid-plate capacity of theaudion. The latter capacity coupling is due to the induction upon thegrid of a charge by the varying plate charge. When the audion filamentisnot heated this is the only coupling of this kind which exists.

When the tube is lighted, however, part of the electric flux from theplate is deflected to the electrons or space charge with the result thatthe efi'ective grid-plate capacity is changed. The general method ofbalancing,

3 either by compensation or neutralization, de-

scribed in my copending application may be used to eliminate thiseffect. A resistance component may sometimes appear, in which ;casea'perfect frequency-independent bal ance can be obtained. only by addingextra resistance in the compensatingor neutralizmg network.

The lncidental couplings, of electromag netic, electrostatic or othertypes, between the apparatus and connecting wlres external to the audionmay be eliminated'by judicious shielding, as is well known to thoseskilled in the art. Since such shielding is general practice it'cannotbeconsidered part of this in vention and is therefore omitted from thediagrams. The coupling between coils can usually be eliminated by aproper geometric arrangement, or by surrounding the coils by a coppershield of sutficient thickness. The

proper thickness will be determined by the' extinction coeflicient ofthe metal and the frequency; for example, a thickness of 0.015"

would be indicated for copper orsilver at, 300 meters. r

Thesemethods of rendering the repeater unit completely unidirectionalare illustrated in Figs, 2, 3, 4, 5 and 6. The variety of thesearrangements-is due tothe different methods of eliminating the elfectivecapacity coupling. i a.

Fig. 2 represents a repeater element suitable for interposition betweenan antenna and later oscillatory element. I The method of compensatingcapacity coupling .descrlbed in my oopending'application,Serial Number629,702, and shown in Fig. 4 thereof, is used here. Figs. 2 and 3 differin the.

method of forming the compensating winding. The reference symbols areuniform so that the following escription applies to both circuits. L andL constitute the input transformer tuned by means of the variable taincases.

rangement may be made. The A, B and C' a batteries have theirconventional locations. As described in the copending application justcited, capacity compensation is obtained by bringing point Y to thepotential of'the point X. Point Y is the lower terminal of the inputcircuit, that is, the terminal having thelower alternating currentpotential, or, in general, most closely approaching to the alternatingcurrent potential of the filament. v This might have been done'bydirectly connecting X and Y but an insulating condenser would then havebeen necessary to keep the plate battery voltage 011 the grid. For thisand other reasons .the inductive method shown is to be preferred, sinceit brings Y to the direct current potential of I the filament electrode.The output trans--"' 1 85 former is formed by L, and L which are,

tuned by C In Fig.- 2 the compensation 1s obtained by an extra winding Lin Fig. 3 part ofthe coil L is used for the same pur- .pos'e; This is anexample of a case where 'ing condenser of low impedance,which serves tointrodu e the alternating current plate current through both filamentterminals. R is a resistance which may be used to control the filamentcurrent and incidentally serve in biasing the grid negatively. C.represents a compensating capacity, which may obviously reside betweenthe electrodes of the audion or their connecting wires, or in anexternal condenser. In certain cases it is desirable to add compensatingresistan es R, and R to either C... or G, or both. either in series. asshown in Fig. 2, or in parallel, Fig.

3. The introduction of such resistance or other "balancing elements isin accordance with the principles of my conending application. I includethem in these diagrams for generality; they may be omitted in cer- Fig 4represents a repeater unit suitable for interposition between an antennaand later oscillatory element, specifically a regenerative element. Amodification of the method of compensating the audion capacity coupling,described by Rice in Patent No.

1,334,118 is used. This modification consists among other things in theprovision in. the

plate circuit. of an extra inductance, L,, f

cuit operative. In one specific experimental -whose function is toprevent the circuit from arrangement with L L =200 mchs, oscillationswere obtained in a range of plate circuit inductance extending from 60mchs. to

devised, for example, I may use a condenser shunted by a high impedancechoke-coil, the choke-coil serving to .pass the steady normal platecurrent around the condenser. Special design of the transformer L L willoften accomplish the same result. Referring to the diagram in this'specific example, L and L ..are two inductors or parts of the sameinductor; C2 is a variable condenser for tuning; C is a compensatingcondenser whose capacity is of the order of 10' microfarads;

is a compensating resistance of the order of 10 ohms; 'A is the filamentbattery; B the plate battery and C is the'battery used to bias the gridnegatively to prevent the flow of thermionic current to the gridelectrode; C1 is a filament shunting condenser of low impedance; L L isthe output transformer. The functions of all these parts have alreadybeen explained. Theparticular values of these constants aremerelyillustrative, and my inv'entionis of course not limited thereto. 4

Fig. 5 illustrates a repeater unit in which the audion capacity couplingis eliminated by a neutralization method. The principle of such methodsis disclosed in my copend- -ing application. Referring to the figure, L

and L constitute. the input transformer which is tuned by the condenserC C 1s a compensating condenser; L and L are either separate coils orparts of the same 'coil; L and C3 represent the output circuit;

R 18 a compensating resistance; R is a resistance in the filamentcircuit, the direct current drop across which is used to give the grid asuitable negative bias; the C battery reinforces the biasing efi'ect ofR; the A and B batteries have their conventional circuit locations; C isa filamentshunting condenser of low impedance. The

output circuit, represented by the coil L must be coupled to L and L sothat the effective'impedances between the terminals of L and L are' ofproper value to maintain a' state of balance in the circuit; obviouslyalso the coupling between L L and L must be fixed. It is not necessarythat L and L be coupled together, but their couphngs to L must result inimpedances between their terminals which satisfy the requirements ofneutralization. For best results with tubes of the usual 15,000 ohmsplate resistance the coils L and L, are of small inductance com paredwith that'of L and the coupling between L anad L and between L and L,should be close. In order that persons skilled in the art may reproducemy results, I give the following constants of one specific circuit; L=20 microhenries; L =20 microhenries; L 300 microhenries G 0.00033microfarads 200 weoo meters.

Fig. .6 illustrates a repeater unit in'which an alternative method ofneutralizing the audion capacity coupling is employed. The otherarrangements for eliminating the enumerated couplings other than thatdue to the audion capacity are those already described. L and L are twocoils of preferably tight couplings wound in opposite directions and so4 connected that their noncommon terminal voltages are; opposite inphase; C is a compensating condenser; R

and R are compensating resistances, which 1 makeup the departure of thevoltages of L and L from exact 180 phase relationship and which alsocompensate for the resist anace component of the variable space chargecoupling; R is a filament resistance, the drop C =0.000005' microfarads.1 .These values were found suitable for a unit designed to cover a wavelength range of will be included as the proper design' of 7 this elementis desirable for the eflicient operation of the repeater. Since theoutput will usually be into the grid circuit of another audion, theproblemis that of obtaining a maximum secondary voltage in the coupledcircuit arrangement. Let L L be the primary and secondary inductancesrespectively, and C the secondary capacity. The coupling between L and Lis preferably made unity, in which case the maximum voltage across thesecondary will be obtained when the secondary condenser is tuned sothat:

1 QQEaL (1 L L and C are under the control of the designer. L and C areessentially related by the resonance condition. Usually the amplifierunit will be required to operate over a bandof wave lengths, in whichcase to some extent by the variation of- R with L for a particular .coilconstruction. Once tailed circuit diagram of peater of the type ofFig. 2connected in front former, which with the condenser 0 serves to i thecompensating coil L pensating resistances.

.serves to reduce the L, has been decided upon the optimum L can becalculated from the relation:

R, is the effective secondary resistance; B is the primary resistanceplus the internal plate resistance important to note that in the usecontemplated in this invention, where the repeater element may hesucceeded by element, the secondary resistance R be diminished from itsnormal value by regeneration, so that Formula (2) shows immediately thatL should be made considerably lower than it would be in the case of anormal multistage amplifier. In many cases L may be advantageouslyreduced to a single -turn, or if tighter coupling is desired, a numberof single'turns in par These mathematical conclusions can be directlyapplied to the design of the output transformer in such arrangements asFigs. 2, 3 and 6; in applying them to the arrange ment of Fig. 5, of theload current is carried by the coil L, of Fig. 5. The optimumprimaryinductance is entirely contained in the coil L of Fig. 5. Withthis understanding the principles apply uniformly. i

Specific applications of the invention are shown in Figs. 7 and 8. Fig.7 shows the dea unidirectional reof a regenerative receiver ofconventional type. Anantenna'of ordinary elevated type is shown. Therepeater'unit is so designed that from the point of view of theregenerative receiver its output circuit has electrical resemblance toan without special modification. Referring to Fig. 7, L and L representthe input transtime the antenna; C is a compensating condenser, whichmay be partly external to the audion or be replaced completely by thegridfilament audion capacity; C. is a. filament shuntingcondenser of lowimpedance, which with tubes having high filament resistances,

return current upon is an inductance to which or to part of: which maybe 'ap ro'x1- condenser whose capacity is a mately that of an averageantenna; battery used to tube 1 negatively, and R R are phase com- Inthe regenerative receiver,;L, and C, constitute the tuned input-)circuit'; regeneration is obtained by back-doupling through thetickler coil L as U.'- S. Patent-No. is the detector audion of theregenerative receiver,- 3 and 4 being audio amplifiers coupled throughthe audio transa regenerative the flow of electrons; obviously, therepeater circuits must be balanced with normal filament current itmustbe noticed that .none

antenna, so that the unit can be placed in frontof difierent receivers.

.plete extinction by efiect of the thermionic the grid potential; L

is coupled; G is a bias the grid-of the repeater.

grid

L as in present practice, the regenerative am-' plificatio n wouldchange the current in the ofthe amplifier tube. It is could oscillateinto the antenna and cause antenna and cause extra reradiation, or -itradiation. Both these possibilities areeliminated by the circuit of Fig.7, because by the interpositon of a perfectly unidirectionthe action canbe relayed from grid to plate, but tion. V

'I- have already. pointed out that the efiec-i tive grid-plate capacityof the audion is changed from its therefore,

the filament of the audio heated, with the flowing and normal electrodevoltages impressed: A cold-tube balance will be spurious. In the circuitused in Fig. 7 and Fig. 2, where the grid-filament capacity of theaudion is in the balancingarm of the bridge, the same remarks apply tothe grid-filament capacity. This too .will be subject 'to change by theelectronic current, and since its change will not in general exactlyfollow that of the grid-plate capacity, a .hot-tubebalance will be,required. Since these effects are new I will givethe followingexperimental data concerning them. The constants of one specificrepeater circuit (Fig. 7) were as follows: L =25 microhenries, C==O.00025 microfarads, L comprises 12 microhenries fitting overL. withair. space and located near ground .potential point of L Letting theregenerative receiver oscillate and listening on the antenna sidewith atwo-stage amplifier, it possible to get comv point varies with thefiequency due to ca'. pacity unbalance between L,, and L4 variation ofelectronic component of'finterelectrode capacities. The value of Cvaries consistentlylwith the filament temperature; when filament is litto full brilliancyC is from 5 to 9 microfarads less than for cold tube.I

Fi 8 shows a second embodiment. In this case ftnoil antenna is used, noinput trans formerv being repeater is of the type of Fig. 4. Asuperheterodyne receiver of conventional type suc-' true geometricalvalue by a 4 C The balance and t6- necessary and the unilateral ceedsthe-repeater. This is an example of a 1 true oscillatory. generativeelement,

I the potential of the filament and'batelement rather than a re;-

the object in this case being to prevfint the oscillation generatedlbythe-local osci of this circuit is the same as that of the preceding one.

- While a true unidirectional repeater can be obtained only bycorrecting for each of the disturbing causes noted above, it is apparentthat the amount of feed-back due to the Several causes will vary. withdifferent tubes and to 'a smaller extent with the. circuit in which thetube is employed. 4 In some cases, therefore, a substantially. one-wayrepeater action can be obtained without correcting for .a disturbinginfluence which is ofa negligible value.

I claim: 1.'In a radio receiver, the combination with a currentcollecting deviceand an oscillatory element, of a unidirectionalrepeat--er located between said current collecting device and said oscillatoryelement, said unidirectional repeater comprising the combi- .nation ofan audion tube with means for reducing effects upon the input circuittermi- "'prisin in combination, means the e ects upon the lnput c1rcu1ttermmals nals of variations in potential across the output circuitterminals due to the grid-plate capacity of saidtube, means for reducingthe flow of current from the grid to the filament, means for reducingthe. flow of alternating plate current through the filament, and meansfor reducing incidental couplingbetween elements in the input and outputcircuits of said tube.

2. A unidirectional audion reipeater comor reducing of variations inpotential across the plate circuit load due to the grid-plate capacityof the audion tube and the effects of the charge induced upon the grid'by varying space charge in the tube,-means for reducingthe effects ofthe flow of current from the grid ,to the filament, means for reducingthe effects of the flow of plate current through-the filament, and meansfor reducing the effects of incidental coupling between elements in theinput and output circuits of the tube.

3. A vacuum tube amplifier stage having an impedance network arranged inthe form of an alternating current Wheatstone bridgeof which the inputand output circuits of the stage form. conjugate arms, and of which onebalancing arm comprises capacity between grid and plate, anda secondbalancing arm comprises a reactance and a phase circuit including anoutput transformer of adjusting resistance between grid and filament ofthe vacuum tube.

4. An electrical amplifier comprising a vacuum tube, an input circuit,and an output output transformer, the in'lpeda'nces between plateandfilament of said vacuum tube, one terminal of said input circuit-beingconnected to the grid of said vacuum tube, and the other terminal ofsaid input circuit being connected to a point in the secondary of saidoutput transformer, the impedances between grid and plate and betweengrid and filament of said vacuum tube cooperating with saidoutputtransformer to provide the four balancing arms of an alternating currentWheatstone bridge across which said input and output circuits arearranged as conjugate arms.

5. A unidirectional audion repeater comprising, in combination, meansadapted to reduce effects upon the input circuit terminals of variationsin potential across the output circuit terminals due to the grid-platecapacity of the audion tube, means adapted to reduce efiects' due toflow of current between grid and filament, means adapted to reduce flowof alternating plate current through the filament, and means adapted toreduce'efi'ects of incidental coupling between elements of the inputandoutput circuits.

6. A unidirectional amplifier stage comprising a vacuum tube having acontrol grid, cathode and. plate; circuit elementsproviding an input andan output circuit forsaid loo stage, means for tuning one of saidcircuits to resonance at a desired frequency, means preventing thevarying potential of said outputcircuit from acting through thegridplate coupling to establish variations of po- 5 tential across saidinput circuit, means establis hing a direct current potential betweensaid control grid and cathode to prevent the flow of current betweencathode and gridi means rendering the direct current potentia betweensaid control grid and cathode substantially independent of the flowofspace current through said cathode, and; means shielding the elements ofsaid input and output circuits to reduce incidental couplings to andbetween the samef.

In testimony whereof, I alfix my signature.

STUART BALLANTINE.

